1. Field of the Invention
The present invention relates to a semiconductor package structure comprising a conductive tape which is used to form an electromagnetic interference shield-forming Faraday cage, wherein the Faraday cage incorporates a module lid as the top surface thereof, the conductive tape as the sides and a laminate ground plane(s) or substrate as its bottom. The present invention also discloses a method for fabricating the foregoing semiconductor package structure.
2. Description of the Related Art
Currently, the Federal Communications Commission (FCC) requires that electronics products, which are commercialized, and used in the United States, meet rigorous standards in limiting their emissions of electromagnetic interference (EMI). Hereby, the spectrum of regulated electromagnetic emissions reaches up to 40 GHz; whereby on-chip and on-module signal speeds of 3, 5 and 8 GHz are fairly common. These high-speed signals radiate at up to 10× their signal rates. Semiconductor products evince a larger amount of GHz frequency emissions than ever before; whereby a wide range of chips, extending from server systems to consumer chips, has encountered costly release or approval delays because they have failed the requisite EMI standards.
Normally, electromagnetic radiation (EM) can be contained inside a hermetically-sealed conductive enclosure, however, in the presence of any holes in that enclosure, they will radiate wavelengths less than or equal to twice the length of the opening, such that higher frequencies can escape from smaller holes. Thus, a 10 GHz signal will radiate from holes, which are larger than 15 mm. A bare die or chip on a module has essentially no enclosure, and will radiate freely in an unobstructed manner. Heretofore, a commonly employed solution has been to position a conductive lid upon the chip, and then connect the lid to the ground for the chip. More recently, conductive posts have been introduced between the surface of the laminate substrate and the lid, whereby an 8-post design is employable and halves the size of the aperture, such that a 40 mm package with 8 posts provides a partial shielding for EMI of up to 7.5 GHz. The laminate may be equipped with surface ground pads, whereby the pads are required to have a BGA (ball grid array) located directly beneath wired to ground. In that case, the posts are made of a conductive adhesive material.
Various consumers for the electronic packages are insisting on protection against EMI to levels above and beyond this 7.5 GHz because of the increased frequency content on their chips inside the package and are requesting a solution with an increased number of posts, such as 16. This, however, is problematic on several levels, inasmuch as firstly, each post requires a specific lateral clearance, which makes tighter placement increasingly difficult and driving adhesive and dispense development, while secondly, each post requires a signal BGA to be converted to ground, thereby reducing the allowed signal count for a given package. Finally, discrete posts with gaps between them create a permeable barrier to EM radiation.
Thus, Chung, U.S. Pat. No. 6,136,128, discloses a method of making an adhesive pre-formed lid for electronic devices, which is adapted to reduce or potentially even eliminate EM radiation. However, Chung does not disclose the structure and method pursuant to the present invention, wherein a novel Faraday cage serves as a two-way EM barrier.